1. Field of the Invention
This invention relates to waveguiding structures and, in particular, to structures in which path regions and confining regions are supported on a primary substrate.
2. Related Art
There may be many path regions in a waveguiding structure and complicated path regions are known, eg. in the case of optical switches in which radiation can be transferred from one path to another.
A known form of waveguiding structure comprises a primary substrate on which waveguides are fabricated by depositing waveguide material into grooves in the substrate. In order to facilitate connection between the waveguides and optical fibres, the waveguide material in each groove stops short of an edge of the structure and the ends of the fibres are mounted in the grooves where there is no waveguide material, the core of each fibre then being optically coupled to a waveguide in end-to-end fashion. Such an arrangement is disclosed in "Optical Coupling from Fibers to Channel Waveguides Formed on Silicon" by J. T. Boyd and S. Sriram, published in APPLIED OPTICS, 17 (6), 15th March 1978.
In the arrangement disclosed, the waveguide comprises a polymeric plastics material, polyurethane, which is deposited from solution into the groove. It is clearly useful if connection between a fibre and a waveguide is physically robust. In this case, the polyurethane can also serve as an adhesive to secure the fibre in place.
It is preferable, however, if the materials in which optical components are fabricated are of the same material system. This, inter alia, facilitates fabrication. Since waveguiding structures are advantageously based on silicon, for instance, so that they can be integrated with devices, it would be advantageous to avoid the use of plastics materials as the waveguide material, and instead to use silicon based waveguide material.
It has been realised, in making the present invention, that it is possible to use waveguide material having a structure coupled to an optical fibre or fibre tail, while still obtaining a sufficiently robust component for practical application which is also relatively easy to fabricate.
A waveguiding structure based on a silica waveguide coupled to a fibre is disclosed in "Fusion Splicing between Deposited Silica Waveguides and Optical Fibers" by N. Shimizu, published in ELECTRONICS AND COMMUNICATIONS IN JAPAN, September 1984, No. 9. In this disclosure, mechanical robustness and low coupling loss are obtained by fusion splicing the fibre to the waveguide. However, the assembly process is complicated by the alignment procedure, for aligning the fibre and the waveguide, which relies on optimisation of transmitted power prior to the fusion splicing step.